Introduction

This article basically illustrates the concept of Data type synonyms which are included in SQL Server 2005 for SQL-92 compatibility.

What are Data Type Synonyms?

Data type synonyms can be used instead of the corresponding base data type name in data definition language (DDL) statements, such as CREATE TABLE, CREATE PROCEDURE, or DECLARE @variable. However, after the object is created, the synonyms have no visibility. When the object is created, the object is assigned the base data type that is associated with the synonym. There is no record that the synonym was specified in the statement that created the object.
All objects that are derived from the original object, such as result set columns or expressions, are assigned the base data type. All subsequent metadata functions performed on the original object and any derived objects will report the base data type, not the synonym. This behavior occurs with metadata operations, such as sp_help and other system stored procedures, the information schema views, or the various data access API metadata operations that report the data types of table or result set columns.

FirstName is actually assigned an varchar(20) data type, and all subsequent metadata functions will report the column as an varchar(20) column. The metadata functions will never report them as a character varying(20) column.
Similarly, LastName is an nvarchar(20) data type column and Makes is a float column.

Conclusion

This is an introduction to the Data Type Synonyms in SQL Server. The idea is to get familiar with another way of writing DDL queries using Data Type Synonyms.

Reference

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